1. The Field of the Invention
The present invention relates generally to microneedles for the injection and extraction of fluids. More specifically, the present invention relates to an easily fabricated, micromachined array of microneedles or a single microneedle which can be easily attached to a syringe and which are mechanically durable.
2. The Relevant Technology
Micro instrumentation is a rapidly growing area of interest for a broad spectrum of engineering applications. One particularly fast growing area is biomedical instrumentation where significant efforts are being made to develop micro biochemical analysis systems, physiological systems, and drug delivery systems. A variety of manufacturing technologies are used to fabricate these micro systems, many of which are categorized under the set of technologies known as micromachining. The number of biomedical applications for micromachining technologies is rapidly growing. Since micromachining technologies are relatively new, there is an increasing set of manufacturing techniques and critical applications still to be addressed.
In many areas of biotechnology and medicine, there exists the need for fluid injection on a microscale; either for injection into a precise location, or for injecting small amounts of fluid. It is advantageous to be able to perform an injection with a minimal amount of tissue damage, and also with a minimum amount of discomfort and pain to patients. Microneedles and microneedle arrays are capable of performing these tasks. Some of the smallest hollow needles that are currently available have inner diameters of over 200 μm. Prior microsized (sizes on the order of microns, where 1 micron=1 μm=10−6 m) needles have been made, as in U.S. Pat. No. 5,457,041 to Ginaven et al., and U.S. Pat. No. 5,591,139 to Lin et al.
For some applications, it is desirable to inject small amounts of fluid; however, in other situations, larger amounts of fluid are required to be injected. Most of the prior systems do not have the capability to transmit large amounts of fluid into a precise location. One of the methods used to address this problem is to fabricate an array of needles, as in U.S. Pat. No. 5,457,041 referred to hereinabove. The patent to Ginaven specifies an array of microneedles of about 20 needles by 20 needles, wherein the length of the needles is between 10 and 25 microns, and the spacing between needles is between about 5 and 20 microns.
Problems with prior microneedles include relatively poor mechanical durability. This is mainly due to the fact that such microneedles have been made out of etched silicon or out of chemical vapor deposited polysilicon, both of which have a tendency to be brittle and break easily.
It would therefore be of substantial interest to develop a durable device which is capable of injecting precise quantities of fluids into specific locations with a minimal amount of tissue damage, and which overcomes the difficulties associated with prior microneedle devices.